dired-dwim-target

dired-dwim-target is a variable defined in `dired.el'.
Its value is

nil

Documentation:
If non-nil, Dired tries to guess a default target directory.
This means: if there is a Dired buffer displayed in the next
window, use its current directory, instead of this Dired buffer's
current directory.

The target is used in the prompt for file copy, rename etc.

You can customize this variable.